Method to produce a fabric strip, especially for a screen printing form, and fabric, especially screen printing fabric

ABSTRACT

A cloth web is prepared by providing a plastic cloth with a metallic casing layer on both sides thereof by vapor deposition, plasma spraying or cathode sputtering, and then galvanically coating the resultant material with a metal coating.

This is a national stage application of PCT/EP97/104844 filed Sep. 6,1997.

The invention concerns a process for the production of a cloth web, inparticular for use as a screen printing form comprising a non-metalliccloth which is provided with a casing layer and then galvanically coatedwith a metal coating. The invention also concerns a cloth comprisingmutually crossing strands, in particular a screen printing clothproduced by that process.

Centuries after it was first used in China the screen printing processhas been known in Europe approximately since the 19th Century; afine-mesh textile cloth or wire mesh material is stretched out in ascreen printing frame and covered at the image-free regions so as to beimpermeable to ink. Besides manual cut stencils—for example forlabelling or writing—nowadays preferably photographically produceddirect or indirect stencils are the usual practice; the choice of thekind of stencil adopted—in the case of direct stencils those withemulsion, with direct film and emulsion or with direct film and water—isleft to the discretion of the screen printer.

A plurality of steps are usually required to produce a screen printingform. Firstly a screen printing cloth is stretched out over a clampingframe of light metal or alloy, wood or the like, and is glued to theframe in its stretched position. Cleaning of the cloth permits thesubsequent application of a photosensitive emulsion, for example using acoating channel manually or by machine with an automatic coatingapparatus. As the coating thereon cannot be produced exactly as far asthe inward side of the frame, the remaining surface area must besubsequently sealed off using screen filler. The coated surface is nowexposed by means of a copy original (film) corresponding to the printimage. The regions of the print image which are not exposed are washedout. After the operation of drying the stencil, a retouching operationis effected, and the edges are covered over with screen filler.

For certain areas of use, it is known, when dealing with plastic meshes,to settle palladium nuclei or seeds on the surface by a chemicaltreatment of the surface, and to metallise the filaments. Those chemicaltreatment procedures involve a plurality of stages and are to be matchedin terms of their compositions and operating procedures to therespective plastic material involved. Limitations in regard to thechoice of material are predetermined on the basis of poor or unsuitablematerials. The known expensive preliminary treatments can be followed byexpensive chemical metal deposition processes; because of its inadequateconductivity, the pre-treated plastic cloth surface cannot be directlycovered with a galvanic metal deposit.

U.S. Pat. No. 1,934,643 dating from the year 1930 describes a cloth ofelectrically conductive material, the surface of which is provided witha non-metallic cover layer or a cover layer of pure metal or an alloy,in particular with nickel or chromium, using spraying, plating or achemical or galvanic process.

U.S. Pat. No. 4,042,466 discloses a process for the production of acloth web which is produced for use as a screen printing stencil from atextile cloth, the cloth web being provided with a metallic cover layer.For that purpose the plastic yarns are coated with a thin metal layer offor example copper of a layer of 1 to 2 μm as a conductive intermediatelayer and a nickel layer of 25 μm is applied thereto by galvanization.

Finally DE 32 43 190 A1 is concerned with a continuous process for theproduction of metallized textile flat structures which are coated withan electrically conductive metal layer and then galvanically reinforced.The first metal layer can be applied by means of a wet-chemical,current-less process or by vapor deposition. The result obtained is ametallized, textile surface structure with still textile properties.Gluing of the mesh intersections is undesirable.

In consideration of that state of the art, the inventor set himself theaim of so improving the process as set forth in the opening part of thisspecification that, while avoiding the known disadvantages,operationally reliable cloth webs are produced inexpensively, inparticular for use in screen printing, under a high loading they resultin a substantially lesser degree of stretch in comparison with the stateof the art, and they can no longer be displaced or deformed. Theinvention seeks to provide that expensive metal cloths can be replacedby metallized plastic cloths of corresponding properties.

That object is attained by the teachings of the independent claims; theappendant claims set forth advantageous developments.

In accordance with the invention a plastic cloth is prepared from bothsides thereof in a multiple procedure by vapor deposition or so-calledsputtering—using cathodic atomisation—for the galvanization operation,that is to say it is provided with a metallic casing layer of a surfaceresistance of 0.2 ohm/2 to 200 ohm/2 and is then galvanically coated.

Finally, such a preparation procedure by means of vacuum plasma sprayingis also in accordance with the invention.

In accordance with the invention all vapor deposition materials can befreely selected and are to be matched to the subsequent galvanizationprocedure. However nickel in particular is preferred because of itschemical resistance; other substances which are advantageously used hereare gold, silver, copper, steel or a light metal—in particularaluminum—alone or as an alloy.

The vapor deposition, sputtering process or spray process is to beimplemented on both sides, and it can also be repeated a plurality oftimes. In that respect, layer thicknesses of about 5 to over 200nanometers—in particular over 50 nm—, are produced.

Electrical conductivity of the cloth is afforded by the dry process stepof vapor deposition, cathode sputtering as mentioned above or vacuumplasma spraying.

The mechanical properties of the metallized cloth are primarilydetermined by the galvanization operation; stretching is strikinglyreduced, with an increased level of strength of the cloth,and—irrespective of the nature of the initial cloths—the resistance toslip of the cloth is increased to an extraordinary degree. Themetallizing substances contribute in particular to the strength at thebonding locations of the cloth of plastic base materials and form aconductive surface. It thus becomes possible to replace expensivemetallic cloths by metallized plastic cloths with similar properties.

Therefore, the basis used for the screen printing form which is producedin a finished condition and which is provided with a coating is ametallized plastic cloth, preferably with a metal coating of nickelbecause of its general strength. The metallic surface of the screenprinting plate reduces the wear of the stencil, whereby it is possibleto achieve very high numbers of print copies with the latter. Theconductive surface of the screen printing plate prevents static chargingphenomena. Limitations in regard to materials to be printed or inks, dueto problems with static, can be practically eliminated.

The metallized plastic cloth according to the invention guarantees veryminimal stretch phenomena with an adequate level of basic strength andprovides that there are scarcely measurable register differences on thestencil, irrespective of the set clamping tension.

The fact that the limitedly flexible metallized cloth is coated over itsfull surface area provides for a high, reproducible stencil quality withexcellent edge sharpness and accurate ink metering. A protective foilwhich is applied if necessary reduces improper manipulation operationswhich could cause impairment of the quality of coating. As the coatingis effected on the endless roll of cloth, there is no need for coveringoperations, as are the conventional practice at the present time.

To sum up, the advantages achieved are as follows:

the metal vapor deposition operation, the sputtering operation or thevacuum plasma spraying operation on cloths—in particular plasticcloths—is effected inexpensively and continuously and provides aconductive casing layer as a basis for subsequent galvanicmetallization, without the occurrence of by-products or waste productswhich would have to be removed for disposal thereof;

without involving specific process adaptation, any plastic basematerials can be used for the metal vapor deposition or sputteringprocedure, for example polyethyleneterephthalate (PET), polyamide (PA),polyethylene (PE), high performance polyethylene (HPPE), or the like;

the vapor deposition materials can also be practically freely selectedand can thus be adapted for example to a subsequent galvanizationprocedure;

the galvanic metal deposition which can be freely determined in regardto its thickness of application can occur directly onto the casinglayer;

the metallized plastic cloths produced in that way have a substantiallylower degree of stretching with a higher level of load-bearing capacityand thus afford similar stretch and load-bearing properties to steelmesh; and

the meshes of the cloth can no longer slide or be deformed, by virtue ofthe metallization, that is to say tension in a yarn direction does notresult in deformation of the cloth—very open-mesh cloths retain theirmesh geometry, under a mechanical loading.

The invention admittedly serves in particular for the production of ascreen printing stencil, but cloths can also be treated in the describedmanner for other uses, in particular filter cloths or surface or flatelements for screening or shielding purposes in the electronics sector.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention will beapparent from the following description of a preferred embodiment andwith reference to the diagrammatic drawing in which:

FIG. 1 is a view in cross-section through a cloth,

FIG. 2 is a perspective view of an enlarged part of the cloth, and

FIG. 3 shows a part of FIG. 2 on an enlarged scale, with a perspectiveview onto a bonding between two mutually crossing yarns.

A cloth 10 for the production of screen printing stencils is producedfrom mutually crossing warp threads or yarns 12 and weft yarns orthreads 14, as shown in FIG. 1 in a so-called linen or basket weave, inwhich two warp threads 12 and two weft threads 14 belong to a respectiverepeat—namely, a unit of repetition which is fixed by a given number ofbonding locations as indicated at 16. The threads 12, 14 can compriseany plastic base materials, for example polyamide (PA), polyethylene(PE), polyethyleneterephthalate (PET), or the like.

The plastic cloth 10 is subjected continuously, as a roll, to a vapordeposition process, the maximum web length being determined by thelargest possible winding diameter in the vapor deposition installation.

The vapor deposition material used is for example gold, silver, copper,nickel, steel, aluminum or the like precious, non-ferrous, heavy orlight metals—each alone or in combination—,more specifically, in such away as to be matched to the subsequent galvanization operation.

The vapor deposition or sputtering operation—or possibly also vacuumplasma application—is effected on both sides and is possibly repeated aplurality of times, for special requirements. In that operation, acasing layer 18 of a layer thickness b of about 50 to over 200 nm, whichis clearly shown in FIG. 3, is produced around the threads 12, 14 eachas a respective plastic core—which is identified in FIGS. 2 and 3 byreferences 12 _(a) and 14 _(a) to distinguish them from the warp andweft threads 12 and 14 respectively for the sake of enhanced clarity ofthe drawing—of a diameter a of for example 15 μm to 100 μm; depending onthe type of cloth and the kind of vapor deposition, the casing layerscan involve surface resistance values of below 0.5 ohm/2 to over 100ohm/2.

That dry coating operation can also result in accumulations of materialin the region of each bonding 16, one such bonding being indicated at 20in FIG. 3 between the mutually crossing threads 12,

Direct galvanic metal deposition can now be effected on the plasticcloth which has been prepared by vapor deposition in the above-describedmanner. In the galvanic application procedure, once again any metals canbe used such as for example Cu, Ni or the like.

The vapor deposition material and the vapor deposition thickness are tobe matched to the subsequent galvanizing process in order to prevent thecasing layer 18 from being reduced by the galvanic bath, whereby theconductivity of the vapor deposition would be reduced or eliminated inthe event of prolonged exposure times. Combinations for galvanicmetallization are inter alia as follows:

a Cu-vapor deposition with a surface resistance of about 0.5 to 1 ohm/2for subsequent galvanic nickel-plating, or

steel vapor deposition with a surface resistance of about 0.4 ohm/2 to10 kohm/2 for subsequent galvanic nickel-plating.

The galvanic metallization operation can be implemented as a continuousprocedure with practically any roll length and results in a closed metalcoating 22 of selectable layer thickness e—of preferably 2 μm to 20 μmand more—over the entire cloth 10; that metal coating 22 provides bothfor a high level of mechanical stability, in particular slip resistance,and also for chemical resistance on the part of the metallized cloth 10;as stated, its strength is considerably increased, with a considerablereduction in stretchability.

What is claimed is:
 1. A process for the production of a cloth web,which comprises: providing a plastic cloth of mutually crossing plasticcloth strands with a plurality of metallic casing layers on both sidesthereof by means of one of vapor deposition, plasma spraying, or cathodesputtering, so that the metallic casing layers have a surface resistanceof about 0.2 ohm/2 to 200 ohm/2 and a thickness of between about 5 and200 nm; and then galvanically coating the resultant material with ametal coating.
 2. A process according to claim 1, including providingsaid metallic casing layers by said vapor deposition.
 3. A processaccording to claim 1, including providing said metallic casing layers bysaid cathode sputtering.
 4. A process according to claim 1, includingproviding said metallic casing layers by said plasma spraying.
 5. Aprocess according to claim 1, including providing said mutually crossingplastic cloth strands with a metallic casing layer of copper by saidvapor deposition, and subsequently galvanically nickel-plating theresultant material, wherein a surface resistance of about 0.5 to 1 ohm/2is produced in the vapor deposition layer.
 6. A process according toclaim 1, including providing said mutually crossing plastic clothstrands with a metallic casing layer of steel by said vapor deposition,and subsequently galvanically nickel-plating the resultant material,wherein a surface resistance of about 0.4 ohm/2 to 10 ohm/2 is producedin the vapor deposition layer.
 7. A process according to claim 1,wherein said metallic casing layers include at least one of gold,silver, nickel or copper.
 8. A process according to claim 7, whereinsaid at least one of gold, silver, nickel or copper is in the pure formof the metal.
 9. A process according to claim 1, wherein the metalliccasing layers include at least one of nickel, chromium, steel oraluminum.
 10. A process according to claim 1, wherein said metalliccasing layers have a thickness of between about 50 nm and 200 nm.
 11. Aprocess according to claim 1, including providing said galvanicallyproduced metal coating enclosing the casing layers, with a layerthickness of said galvanically produced metal coating being from about 2μm to about 20 μm.
 12. A process according to claim 11, includingproviding nickel as the galvanically produced metal coating.
 13. Aprocess according to claim 1 for the production of a cloth web for useas a screen printing form.
 14. A cloth web comprising a plastic cloth ofintersecting plastic cloth strands provided with a plurality of metalliccasing layers on both sides of said plastic cloth by means of one ofvapor deposition, plasma spraying or cathode sputtering, with themetallic casing layers having a surface resistance of about 0.2 ohm/2 to200 ohm/2 and a thickness between about 5 and 200 nm, wherein saidmetallic casing layers are in turn covered with a galvanically coatedmetal coating.
 15. A cloth according to claim 14, wherein the metalliccasing layers contain at least one of gold, silver, nickel, copper,chromium, steel or light metal.
 16. A cloth according to claim 14,wherein the thickness of the metallic casing layers are between about 50and 200 nm.
 17. A cloth according to claim 14, wherein the galvanicallycoated metal coating on the metallic casing layers have a thickness ofbetween about 2 μm and 20 μm.
 18. A cloth according to claim 14 for useas a screen printing form.
 19. A cloth according to claim 14 for use asa filter cloth.
 20. A cloth according to claim 14 for use for shieldingpurposes in an electronic sector.